This invention relates to writing wicks for felt markers or pens. Such marker wicks are generally made from a bundle of individual monofilament thermoplastic strands in a known manner so that separate and isolated longitudinal capillary channels or chambers are formed between the individual strands. Thus, the individual strands are merged along the direction of the longitudinal axis of the wick in such a way that the longitudinal capillary chambers are not mutually interconnected. That is, the chambers or channels are sealed from each other and from the outside.
It has been found that writing wicks of this type exhibit considerable variation in writing characteristics and qualities due to unavoidable manufacturing tolerances. For technical and economic reasons these tolerances can be reduced only to a certain acceptable minimum but not to an absolute minimum. The factors which influence these tolerances involve a number of considerations. For example, the raw material from which the wicks are made is of importance, particularly the melting point and moisture content have to be considered. The control of the extruder, of the heating zones, and of the temperature as well as the pressure and r.p.m. of the spinning pump influences the writing quality of such wicks. Other factors include the variable degree of contamination of the screens and the control of the temperature of the spinneret head upstream of the spinneret plate as viewed in the fiber flow direction. Downstream of the spinneret plate the variations in the filament withdrawal tension and in the temperatures of the heating and cooling baths may influence the quality of the filament. The foregoing factors superimpose or combine with one another in a multiplicity of statistical variations so that the end product may exhibit random characteristics within an operating range defined by maximum and minimum values which are still acceptable.